This invention relates generally to machinery for the manufacture of plastic pipe, and more particularly to a machine capable of forming more than just one diameter of an improved pipe structure which features a pipe wall with apertures therein when the pipe is examined in cross-section.
Plastic pipe has found a variety of uses especially relating to drainage. One of the concerns in the manufacture of plastic pipe is the amount of raw materials consumed and the resultant weight of the finished product. For example, 48" interior diameter solid wall plastic pipe weighs approximately 200 lbs per foot. It has recently been discovered that plastic pipe having apertures formed therein, when the pipe is viewed in cross-section, weighs approximately 30 lbs per linear foot. However, a problem exists in designing a machine capable of manufacturing pipe having the desired cross-section. Another of the concerns in the manufacture of plastic pipe is the attendant costs associated with the manufacturing equipment.
In general, extruded plastic pipe is formed on a production line having a variety of specific machines incorporated into the manufacturing process. One of the first machines is an extruder. Plastic powder, or more preferably pellets, is fed through the extruder where it is subjected to high temperatures such that the plastic melts. The plasticized plastic then proceeds through a feed tube, at the end of which the plastic enters into a typically drum shaped die. At the front of the die is the specific cross-section profile to be extruded. As the hot plastic comes out of the die, it passes over what are called calibrating or calibration fingers which assist in maintaining the desired cross-sectional form which has been extruded. These calibration fingers are part of the manifold assembly. The rest of the manifold assembly extends from above the die to well beyond the calibration fingers. In addition to the extruder and die, which is supported on a die post assembly, plastic pipe is manufactured using a former or forming head.
Prior art manifold assemblies have apparently limited the ability to manufacture a plastic product having a cross-section which incorporates apertures. It is thus apparent that the need exists for an improved manifold assembly which manufactures a product having the desired cross-section.
Additionally, until now, the former assemblies used to manufacture plastic pipe have been a very limiting factor in the manufacture of such pipe. For example, 48" interior diameter plastic pipe is very popular for large civil engineering applications. Existing prior art formers for manufacturing such pipe can basically make pipe of approximately that dimension, but the specific dimensions that ultimately result often depend on the specific type of plastic used. Attempting to "fine tune" the diameter of large diameter plastic pipe is not realistically possible.
Even more importantly however, is the fact that 42" pipe is also popular, and that in the existing art, to make pipe of that diameter requires an additional complete former assembly: a costly capital investment. There are other popular sizes of large diameter plastic pipe, namely 30", 36", 54" and 60", all of which sizes until now have required separate former assemblies as a condition for their manufacture. Thus it can be appreciated that for a company to manufacture the four most popular sizes of large diameter plastic pipe, it has been necessary to invest in at least four former assemblies. Even then, the manufacturing tolerances associated with the pipe formed on such machines is relatively large, since there has been no means to minutely adjust the diameter of the pipe as it is initially being formed.
Prior art former assemblies have been relatively limited as to their ability to manufacture more than just one diameter of plastic pipe, with that pipe having to have relatively large tolerances associated therewith. It is thus apparent that the need exists for an improved former assembly which manufactures a product having more than just one of the desired diameters of large diameter plastic pipe, and moreover a product whose diameter can be minutely adjusted.